Method for producing flat products made of aluminum alloys

ABSTRACT

A method of producing flat products in aluminum alloys comprising:
         A) cold rolling to a hardened condition:   B) applying a short-time ion beam surface treatment; and   C) repeating steps A and B until a flat rolled product of a specified thickness is obtained.
 
The surface treatment is preferably performed using an ion beam of atomic mass A≧10 amu having a power of between about 20-40 keV and an ion current density of between about 0.1-1 mA/cm 2  for from about 5 to about 200 seconds. In the process of irradiation flat products may be continuously and uniformly displaced with respect to the ion beam.

FIELD OF THE INVENTION

The present invention is related to aluminum metallurgy, and moreparticularly to a novel method for alleviating the hardened (coldworked) condition that requires stress relieving and structureimprovement during conventional processing.

BACKGROUND OF THE INVENTION

The role of aluminum alloys as structural materials is constantlyincreasing. In addition to commercial pressures to improve the physicalproperties of aluminum alloys, recent adverse economic conditions haveimposed additional pressures on reducing production costs.

One of the most labor intensive and power consuming operations in themanufacture of flat rolled aluminum alloys are those operations relatedto the necessity to relieve the hardened (cold worked) conditionoriginating in the course of cold rolling. Hardening or cold working inthis context describes a condition wherein flat rolled aluminum hardensin the course of cold rolling. This hardening results in ductilityreduction that makes further rolling impossible. In order to eliminatethis phenomenon flat product is typically subjected to heat treatment ina specified range of temperatures intermediate the various individualrolling procedures.

A conventional method for producing flat rolled aluminum alloys isdescribed in Structure and Properties of Semi-Finished Products inAluminum Alloys. Reference book ed. by V. A. Livanov, Moscow,“Metallurgiya”, Page 85, 1974. This process includes cold rolling to thehardened condition and heat treating (intermediate annealing), as thesesteps are repeated to produce flat rolled products of a requiredthickness. Anneals are carried out at temperature of 310-335° C.According to this method the best anticorrosion properties are providedby slow heat up through the annealing cycle and subsequent slow cooling.Annealing is achieved by placing coils or stacks of cut aluminum alloysheets into an annealing furnace for heat treatment. Such handlingresults in the consumption of large amounts of time and powerconsumption that translate into high costs of production. One of themost labor intensive steps during performance of these annealingoperations is the removal of rolled coils from the hot rolling mill,coil transportation and placement into and removal from the annealingfurnaces. The smaller the gauge of the flat rolled product beingproduced, the larger the number of anneals required.

The obvious disadvantages of this method are the high labor cost andenergy intensiveness of the process. Another less apparent disadvantagerelates to the impossibility eliminating some intermetallic compoundsthat originate in the course of annealing, for example the formation ofAl₆ (Fe, Mn). The existence of coarse intermetallic compounds such asAl₆ (Fe, Mn) in the alloy structure negatively influences the propertiesof the cold rolled material, in particular, it reduces its ductility.

A method of producing cold-work parts from the following alloycomposition is known (A 2001124821, MPK7, B22F3/24, C21D1/26, C21D7/02,C22F1/10, C22F1/18).

This method used for the processing of alloys chosen from those of iron,nickel, and titanium aluminides, includes the following steps:

(a) producing a part, which is hardened by metallic alloy compositionhardening to such an extent, that a face-hardened zone is created on it;

(b) heat treating the face-hardened part by heating in a furnace in sucha way, that it is instantaneously annealed in less than one minute;

and optionally (c)—reiteration of steps (a) and (b) until a part of aspecified gauge is produced.

One of the variants of this method includes instantaneous annealing byheating the hardened part with infra red (IR) radiation.

Hardening is induced by cold rolling, and hardened parts, in particular,sheets, strips, extruded rounds or strip profiles or wires are treatedin accordance with this technique. The step of instantaneous annealingconsists of heating the hardened part to a temperature of at least 400°C. during of minimum 45 sec. using IR radiation.

Though heating and holding in a furnace according to this prior artmethod takes less than one minute, parts must still be delivered to thefurnace, where the high temperature must be maintained to realizeinstantaneous heating. All of these steps incur expenditures of time,labor, and electric power.

In the course of this prior art process the hardened condition isrelieved only in the face-hardened zone, and it is also impossible toeliminate the formation of some intermetallic compounds such as, Al₆(Fe,Mn) in the application of this prior art process to more conventionalaluminum alloys.

Thus, there remains a need for a method for the elimination/alleviationof cold work during cold rolling that is more cost effective than theprior art annealing processes that require large expenditures of time,labor and heat energy to achieve.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor annealing or relieving cold work in the course of processingaluminum flat rolled or otherwise processed products that eliminates thecostly thermal annealing steps of the prior art.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method ofproducing flat products in aluminum alloys comprising:

A) cold rolling to a hardened condition:

B) applying an ion beam surface treatment to relieve cold work inducedhardening; and

C) repeating steps A and B until a flat rolled product of a specifiedthickness is obtained.

The surface treatment is preferably performed using an ion beam ofatomic mass A≧10 amu having a power of between about 20-40 keV and anion current density of between about 0.1-1 mA/cm² for from about 5 toabout 200 seconds. In the process of irradiation flat products may becontinuously and uniformly displaced with respect to the ion beam.Aluminum alloys of the Al—Mg system, which contain 5.8-6.8 wt % Mg(so-called, magnaliums), the Al—Cu—Mg system containing Mn additives(duralumins) and the Al—Li—Cu—Mg system with lithium contents of 1.8-2.1wt % are particularly, but not exclusively, susceptible to the annealingpractices described herein.

DETAILED DESCRIPTION

According to the present invention, irradiation is conducted by an ionbeam with a power of 20-40 keV, an ion current density of 0.1-1 mA/cm²for from about 5 to about 200 seconds. In the process of irradiationflat products may be continuously and uniformly displaced with respectto the ion beam. Surface irradiation may also be carried outsimultaneously from two sides.

The chemical composition of some, but not all, susceptible aluminumalloys (wt %) are presented in Table 1 below.

TABLE 1 Si Fe Cu Mn Mg Zn Ti Li Be Zr Ni VD1 0.7-1.2 0.7 1.8-2.6 0.4-0.80.4-0.8 0.3 0.1 — — — — 1441 0.08 0.12 1.5-1.8 0.001-0.10  0.7-1.1 —0.01-0.07 1.8-2.1 0.02-0.20 0.04-0.16 0.02-0.1 AMg6 0.1  0.1 <0.1 0.696.4 <0.1 0.04 0.0008 — —

The duration of ion beam irradiation is specific to alloy composition,processed sheet thickness, and is affected by whether the sheet istreated on one or two sides. In addition, it is important to note thatthe time of irradiation necessary for obtaining appropriate treatmentdepends on ion beam current density. The higher ion beam currentdensity, the shorter the time of irradiation.

Results for stationary and uniformly moving flat product strip areabsolutely identical given identical irradiation parameters.

The present method differs from prior art thermal annealing practices,as well as from past ion-beam treatments in the fact that it uses aradiation-dynamic action by accelerated ions instead of normal heattreatments or ion alloying processes that can induce radiation damage.

In this context, it is noted that ion beams of low and medium energyions (from several units to several hundreds of keV) have been used forthe purpose of surface alloying (ion penetration into layers withthicknesses from several tens to several hundreds of nm), and also toestablish highly defective (strongly nonequilibrium—up to amorphous)conditions in surface layers of the same thickness allowing: increasesin corrosion resistance; enhancement of microhardness; wear resistance;as well as modification of some other surface properties of materials(Surface Modifying and Alloying by Laser, Ion, and Electric Beams, adigest edited by J. M. Pote et al., translation from English edited byA. A. Uglov, M., “Mashostroyenie”, p. 424, 1987; Effects of Long-RangeAction in Ion-Implanted Metallic Materials, A. N. Didenko et al., Tomsk,NTL Publishing House, p. 328, 2004). These processes do not produce theannealing effects described herein, but rather induce alternativesurface modifications as just described, and are not used to annealmaterial that has achieved a hardened or cold worked condition.

Accumulation of high-static stress solids in surface layers fromimplanted admixtures (by large radiation doses of more than 10¹⁷ cm⁻²),as practiced in the prior art, allows modifying surface layers up to adepth of several tens of microns at the expense of formation of newdislocations and movement of existing dislocations deep into thesubstance.

We have found that exposure of aluminum alloys to high energy ion beamsinitiates deeply self-propagating structural phase transformationsthereby altering the structural properties of these materials to depthstens and even hundreds of thousands of times deeper than the depth ofpenetration of accelerated ions impacted with and into the surfacethereof. These effects are apparently stimulated by the formation andpropagation of microshock waves formed as the result of atomicdisplacement/compact cascades caused by ion beam irradiation.

Experimentation indicates that irradiation with ions with atomic massA≧10 amu, but lighter than argon, induce similar action on the structureand properties of aluminum alloys, though rather weaker than thoseinduced by argon. Using ions in the range of A<10 amu, the density ofthe energy emitted by the atomic collisions, and, concomitantly, theintensity of radiation-dynamic effects of the ion beams on the structureand properties of the treated aluminum alloys, substantially decreases.

Application of the method of the present invention to an aluminum alloycomprising Al-4 wt % Cu indicates that the particular ion used inirradiation (for example, Ar⁺, Al⁺ or Cu⁺) has relatively no influenceon the structural and phase composition changes induced by the ionirradiation described herein. Thus, selection of the specific heavy ionsused for irradiation is not critical. Utilization of inert gas ions, inparticular, Ar⁺, guarantees lack of any secondary effects on surfacechemical properties and thus use of this ion is specifically preferred.

Lower energy ion beams have been used to clean surfaces of materials ofoxides and adsorbed admixtures due to the effects of cascade and thermalsputtering of surface atoms by ions of lower energies (typically 5-10keV). Ions with energies of 10-20 keV and more, having greater depth ofpenetration into the substance, are used for ion-beam modification of,for example, the surfaces of construction materials. The upper limit ofbeam energies used (typically 40-50 keV) is determined by the necessityto restrict the temperature of materials under treatment, (in the caseof aluminum alloys, a maximum 450° C.). In addition, the design ofindustrial ion accelerators (ion sources), where portability (smallsizes) is a requirement, generally dictates ultimate voltages that donot exceeding 40-50 keV.

The range of useful ion current densities has been determined, on onehand, by the fact that with j<0.05-0.1 mA/cm² (50-1000 mA/cm²)radiation-dynamic effects are generally insufficient to induce thedesired effects. On the other hand, utilization of currents of more than1 mA/cm² result in virtually instantaneous (within several seconds)heating of the aluminum alloy flat product areas exposed to theradiation, and can result in melting of the surface of the material.

The results of mechanical testing of specimens cut out of initiallyhardened, annealed, and irradiated rolled sheets are shown in Table 2below confirm the results previously discussed, namely the relativelydeep alteration of the properties of these materials by ion beamtreatment as described herein. Electron microscope images of thestructures of sheets of different aluminum alloys obtained afterhardening, annealing, and ion-beam treatment (not shown) confirm theseresults.

TABLE 2 Mechanical properties and structure of sheets in industrialaluminum alloys AMg6, 1441, and VD1 after different types of treatmentAlloy AMg6 1441 VD1 Types of σ_(B), σ_(0.2), δ, σ_(B), σ_(0.2), δ,σ_(B), σ_(0.2), δ, treatment MPa MPa % Structure MPa MPa % Structure MPaMPa % Structure Hardening 445 407 9.6 cellular 315.5 296 3.3 cellular255 246 6.5 cellular Industrial 328 178 28 grained 245 134 20 grained 76— 59 grained annealing (within 2 hours) Ar⁺ ion- 335 182 28 grained 218130 19 grained 105 81 43 grained beam treatment

Example 1

Performance of ion-beam treatment in the rolling Al—Mg alloy sheet(so-called, magnaliums).

After the rolling of an AlMg6 until alloy hardening/cold work makesfurther rolling impossible. The surface of the rolled sheet isirradiated with Ar⁺ ions having an energy of 40 keV, and an ion currentdensity of 400 mA/cm². The sheet has a thickness of 4 mm and isirradiated from both sides for a period of 30 seconds

In the course of irradiation continuous monitoring of target temperatureis carried out by means of a chromel-alumel thermocouple. The ultimatetemperature, to which sheets are heated within the short course ofirradiation, does not exceed 400° C.

Mechanical testing of tensile specimens cut out from hardened, annealed,and irradiated sheets was performed at Kamensk Uralsky MetallurgicalWorks J.S.Co. These tests show that as a result of ion irradiation,irrespective of specimen temperature, ductility increases due to asubstantial decrease in alloy/sheet strength. The results of themechanical testing of initial and irradiated specimens in alloy AMg6 aregiven in Table 2. It is obvious that the mechanical properties of sheetsafter ion-beam treatment are close to the properties obtained by thermalannealing.

Electron microscope examinations have been carried out on specimens cutout parallel and perpendicularly to the irradiated surfaces. Theseexaminations have allowed determination that structural changes(reduction of dislocation density, formation of sub-grained, grainedcrystalline structures) and phase transformations (dissolution andformation of intermetallic phases) initiated by ion irradiation takeplace throughout the specimen depth.

Electron microscope pictures of hardened alloy AMg6 show cellularstructures with wide borders between individual cells of a of diameteris 1-2 μm. Large concentrations of round or ellipsoidal intermetalliccompounds Al₆(Fe, Mn) caused by crystallization and with averagediameter of ˜0.5-1 μm are present in the alloy.

Annealing of cold-worked alloy AMg6 at temperatures 310-325° C. for lessthan 2 hours results in the formation of a uniform re-crystallizedstructure with grain sizes of greater than 10 μm It is noted that afterthermal annealing the alloy retains large amounts of coarseintermetallic compounds Al₆(Fe, Mn) of crystallization origin. Similarcompounds have been observed in the initial cold rolled and hardenedcondition.

After ion-beam treatment a coarse-crystalline grained structure isobserved in the alloy. This structure is the same as that observed afterthermal annealing as described above. In addition, after ion-beamtreatment a reduction in the amount of intermetallic compounds Al₆(Fe,Mn) which can negatively influence the ductility of the alloy is noted.

Thus, a direct comparison of the structural and mechanical properties ofalloy AMg6 after thermal annealing and ion-beam treatment shows thatshort-term ion beam irradiation results in the formation of are-crystallized structure that is similar to the structure obtained asthe result of intermediate thermal annealing. Such re-crystallizationresults in a reduction in strength and a concommitant increase inductility, i.e. relief of cold work.

Thus, the ion-beam treatment for sheets in aluminum alloy AMg6 allowsdescribed herein completely relieves cold work and internal stressesarising in the course of cold rolling. Additionally, improvement of flatproduct structure is observed due to a decrease in the amount ofintermetallic compounds Al₆(Fe, Mn) present that can negativelyinfluence the ductility of the alloy.

Example 2

Performance of ion-beam treatment in the course of rolling sheets inaluminum alloy 1441 of system Al—Li—Cu—Mg with lithium content of1.8-2.1 wt %.

After cold rolling to the point that further rolling is impossible (athickness of about 1.0 mm), instead of applying a conventionalintermediate annealing at T=380-420° C. for 2 hours, both surfaces of asheet in alloy 1441 are irradiated with Ar⁺ ions having an energy of 40keV, with ion current density of 400 mA/cm².

The results of mechanical testing of initially hardened, thermallyannealed, and irradiated specimens show that the mechanical propertiesof sheets in alloy 1441 after ion-beam treatment are close to theproperties obtained by intermediate thermal annealing (Table 2).Irregular cellular dislocations with cell central area average diametersof from 0.5 to 2 μm are found in hardened alloy 1441.

After thermal annealing at temperatures 380-420° C. for 2 hours thestructure of alloy 1441 is irregular: there is a co-existence of grainswith diameter 1-2 μm, inside of which high density of dislocations areretained, and equiaxed re-crystallized grains with average diameters of10 and more μm that are free of dislocations. The fraction of the latteris about 70% of specimen volume.

Thus, ion irradiation results in the formation of a uniformcoarse-crystalline grained structure with grain diameters of 10 μm. Asimilar structure is typical for alloys in the re-crystallized(thermally annealed) condition

Thus, as in the preceding example, the results of mechanical testing andelectron microscope examination of alloy 1441 sheet structure shows thatshort-term treatment of work hardened flat product surfaces with an Ar⁺ion beam results in complete cold work relief throughout sheetthickness.

Example 3

Ion-beam treatment in the course of rolling sheets in aluminum alloy VD1(Al—Cu—Mg with Mn additives with reduced content of all components(duralumin of increased ductility).

After cold rolling to a point where alloy hardening makes furtherrolling impossible instead of conventional intermediate annealing bothsurfaces of a VD1 alloy sheet having a thickness of 1.5 mm areirradiated for 30 seconds with Ar⁺ ions having an energy of 40 keV, withan ion current density of 400 mA/cm².

The results of mechanical testing of cold work hardened, thermallyannealed, and irradiated specimens of alloy VD1 show that after ion-beamtreatment a substantial decrease in strength is observed. This lossdecrease in strength approximates that obtained by intermediate thermalannealing (see Table 2).

Electron microscope examination of cold-worked alloy VD1 indicates thepresence of a dislocation grained structure with narrow borders betweenindividual cells. Cell diameter is 0.5-2 μm.

After two-hours thermal annealing at temperatures of 240-250° C. apractically uniform sub-grained structure with sub-grain averagediameters of 0.5-2 μm is formed in the alloy VD1 sheet.

After irradiation a crystalline structure with grain sizes of more than10 μm is found in the alloy. Also, in the course of irradiation,decomposition of the solid solution occurs with the release of a highconcentration of equiaxed phase θ′(θ″) (CuAl₂) particles with diametersfrom 10-20 μm.

The oversaturated solid solution decomposition processes that occursimultaneously with re-crystallization under ion irradiation do notimpede alloy strength decrease-despite the release of a highconcentration of the uniformly distributed strengthening phase. Themechanical properties obtained are similar to those obtained throughintermediate thermal annealing.

Thus, as shown in the foregoing examples, the method of the presentinvention differs significantly and advantageously from those of theprior art.

Significant advantages of the present invention are that it provides amethod of producing flat products in aluminum alloys in a continuouscycle, without process shutdowns, significantly reduces process energyand labor intensity, and also reduces process cycle time.

A further advantage of the present invention is that during cold workingof aluminum products cold work relief can be achieved not only insurface layers but also throughout the thickness of the material. Thetreatment process of the present invention alters not only the hardnessof the surface layers of the material, but also in induces changes inthe macroscopic mechanical properties, such as tensile strength, yieldstrength, and elongation (see Table 2), of the entire material volume.This results not only in the elimination of hardening, but also in flatproduct improvement by means of the dissolution of coarse intermetalliccompounds that can negatively influence properties and may not bedissolved during conventional thermal annealing.

A plasma ion emitter (S 1 No. 2045102, MPK6 H01Y27/04), hereinafterreferred to as the ion source, has been used to accomplish the claimedmethod. The ion source contains a hollow cylindrical cathode, where oneof its ends has a multi-aperture emission window opening, and a pinanode is installed coaxially with the cathode at the other end by meansof a feedthrough insulator. A pin solenoid creating a magnetic field inthe B cavity is installed at an external side of the cathode coaxiallywith the cathode.

A glow discharge generates plasma with high spatial homogeneity in thecathode cavity. Ions are extracted from the plasma along the magneticfield through openings in the cathode end. A heavy-gage beam (>100 cm²)of circular or band cross-section subject to electrode shape is formedby the two-electrode multi-aperture electrostatic ion-optical system.

After actuation gas puffing (10-30 cm³/min) into the ion source andcreation of a weak magnetic field (5 mT) by an external solenoid with ˜3kV voltage supply, a glow discharge in the source electrode system isignited at the intersection of the electric and magnetic fields. Thedischarge current is controlled within limits of 0.2-1.5 A in acontinuous mode of beam generation and 1-10 A in a pulse-periodic modewith current a width of 1 msec and repetition frequency up to 200 Hz.

The ion beam is generated by application of high voltage (up to 50 kV)between the electrodes of the ion-optical system. Beam current controlwithin wide limits is ensured by discharge current monitoring andalteration. In the continuous generation mode, beam current is up to 80mA, in the pulse-periodic mode at the same average current amplitudebeam current may be up to 0.4 A. The pulse-periodic mode ensures acontrollable set of small doses of ion irradiation (10¹³ cm⁻² perpulse).

Flat product surface double-sided treatment is carried out by means oftwo ion beams directed towards each other at the expense of operatingtwo ion sources. The ion source may be as a separate independent device,or as part of the cold rolling mill.

Further examples of the application of the present invention to veryspecific alloys follow.

Example 4

Production of flat rolled of Al—Mg aluminum alloy.

An aluminum alloy having the composition shown in Table 3 below wastreated as described below.

TABLE 3 Component Si Fe Cu Mn Mg Zn Ti Al Content, 0.4 0.3 0.1 0.7 6.350.2 0.05 Remainder wt %

Ingot cast in the alloy shown in Table 3 is processed to produce a flatsheet having a thickness of 6 mm. This sheet is cold rolled to athickness of 4 mm. Further cold rolling is difficult due to thecold-worked condition of the sheet. Both sheet surfaces are irradiatedwith Ar⁺ ions having an energy of 40 keV, and an ion current density of400 mA/cm², by means of the ion source described above. Irradiation iscarried out for 22 sec.

During treatment, the sheet is continuously and uniformly displaced withrespect to the ion beam, i.e. relative to the ion source. As a result ofsuch treatment the cold-worked condition of the sheet and internalstresses induced during cold rolling are relieved completely.

The sheet is again subjected to cold rolling. Taking into account, thatthe maximum degree of deformation of sheets by cold rolling for thisalloy is 30-35% before onset of the cold-worked condition, onthicknesses of 2.5 mm, 1.5 mm, the sheet is again exposed tointermediate short-term (less than one minute, specifically, 10 and 6sec.) ion irradiation. Sheet structure and mechanical properties both inthe cold-worked condition on thicknesses of 2.5 mm and 1.5 mm, and aftercold work relief are similar to the values presented in Table 2.

Final sheet thickness is 1 mm. Thus, flat rolled sheet 1 mm thick isproduced as the result of three steps of cold rolling and threeshort-term (less than one minute) ion irradiations (having replaced 3intermediate thermal annealing processes in an electric furnace attemperature of T=310-335° C. for 1-2 hours, that are conventionallyapplied to produce flat product with thickness of 1 mm in alloy AMg6).

Example 5

Producing flat product in aluminum alloy 1441 of Al—Li—Cu—Mg system. Thechemical composition of this alloy is given in Table 4.

TABLE 4 Component Si Fe Li Cu Mn Mg Ti Zr Al Content, 0.08 0.12 1.9 1.60.05 0.8 0.1 0.1 Remainder Wt %

Ingot cast in the alloy in Table 4 is processed to produce a flat sheethaving a thickness of 6.5 mm. The sheet is then cold rolled in a coldrolling mill to a thickness of 1.5 mm. Further cold rolling isimpossible at this point due to the cold-worked condition of the sheet.

To relieve this cold-worked condition, both surfaces of the sheet areexposed to irradiation by Ar⁺ ions having an energy of 40 keV, and anion current density of 400 mA/cm² for about 6 seconds. Duringirradiation, the sheet is continuously and uniformly displaced withrespect to the ion beam, i.e. relative to the ion source. As a result ofsuch treatment the cold-worked condition of the sheet and internalstresses caused during cold rolling are relieved completely. The sheetis subsequently cold rolled to a thickness equal of 0.5 mm.

Thus, flat product having a thickness of 0.5 mm is produced in a twostep cold rolling process that incorporates one short-term ionirradiation (having replaced intermediate thermal annealing in anelectric furnace at a temperature of T=380-420° C. for 2 hours, asconventionally applied to produce flat product with thickness of 0.5 mmin alloy 1441).

Example 6

Production of flat aluminum alloy VD1.

The chemical composition of this alloy is given in the Table 5.

TABLE 5 Component Si Fe Cu Mn Mg Zn Ni Al Content, 0.9 1.0 3.5 0.4 0.60.7 0.2 Remainder wt %

Ingot cast in the alloy shown in Table 5 is processed using conventionalmethods to a sheet thickness of 7.0 mm. This sheet is then cold rolledto a thickness of 1.0 mm. At this thickness, further cold rolling isimpossible due to work hardening. To relieve this cold-worked condition,both surfaces of the sheet are exposed for 10 seconds to irradiation byAr⁺ ions having an energy of 40 keV, and an ion current density of 400mA/cm². During irradiation, the sheet is continuously and uniformlydisplaced with respect to the ion beam. As a result of such treatmentthe cold-worked condition of the sheet and internal stresses inducedduring cold rolling are relieved completely.

Thus, flat sheet of VD1 having a thickness of 0.5 mm is produced as theresult of two steps of cold rolling and one short-term ion irradiation(having replaced intermediate annealing in an electric furnace attemperature of T=240-250° C. for 2 hours as is conventionally applied toproduce flat product with a thickness of 0.5 mm in alloy 1441).

Thus, what has been described is a new and highly productive method ofproducing flat product in aluminum alloys which method providessignificant reductions in energy usage and greatly reduces productionexpenditures, all while improving the structure and properties of thealloys. Energy consumption for conventional industrial thermal annealingof flat products in aluminum alloys in the course of rolling isestimated at about 396 kWh per 1 MT of metal, while energy consumptionby the improved ion beam annealing process of the present invention isestimated at about 123 kWh per 1 MT of metal. This is a significant costsaving even ignoring the time and labor savings previously described.

As the invention has been described, it will be apparent to thoseskilled in the art that the same may be varied in many ways withoutdeparting from the spirit and scope thereof. Any and all suchmodifications are intended to be included within the scope of theappended claims.

1) In a process of producing aluminum alloy sheet including a pluralityof cold rolling steps and including an intermediate thermal annealbetween cold rolling steps when the aluminum alloy sheet becomessufficiently work hardened as to inhibit further cold rolling, theimprovement comprising substituting an ion beam irradiation of thealuminum alloy sheet for the intermediate thermal anneals. 2) The methodof claim 1 wherein the ion beam comprises a beam of ions of atomicweight of A≧10 amu having an energy between about 20 and 40 KeV and acurrent density of between about 0.1 and 1 mA/cm². 3) The method ofclaim 2 wherein the ion beam irradiation is carried out for a period offrom about 5 to about 200 seconds. 4) The method of claim 3 wherein thecold rolled aluminum sheet is continuously and uniformly displaced withrespect to the ion beam during ion beam irradiation. 5) The method ofclaims 1 wherein the cold rolled aluminum alloy sheet has two opposingsurfaces and the ion beam irradiation is performed simultaneously onboth sides of the flat product. 6) The method of claim 1 wherein thealuminum alloy sheet comprises an Al—Mg alloy containing from about 5.8and 6.8 wt % Mg. 7) The method of claim 1 wherein the aluminum alloysheet comprises an Al—Li—Cu—Mg alloy which contains between about 1.8and 2.1 wt % of lithium. 8) The method of claim 1 wherein the aluminumalloy sheet comprises an Al—Cu—Mg alloy that includes Mn additives. 9)The method of claim 1 wherein the ion beam comprises a beam of Ar⁺ ions.10) The method of claim 2 wherein the ion beam comprises a beam of Ar⁺ions. 11) The method of claim 3 wherein the ion beam comprises a beam ofAr⁺ ions.